118 LIGHT SCIENCE FOR LEISURE HOURS. 



The narrow straits between Greenland on the one 

 side, and Ellesmere Land and Grinnell Land on the 

 other, are completely ice-bound. "We cannot suppose 

 that the tidal wave could have found its way beneath 

 such a barrier as this. " I apprehend," says Captain 

 Maury, "that the tidal wave from the Atlantic can 

 no more pass under this icy barrier, to be propagated 

 in the seas beyond, than the vibrations of a musical 

 string can pass with its notes a fret on which the 

 musician has placed his finger." 



Are we to suppose, then, that the tidal waves were 

 formed in the very sea in which they were seen by 

 Kane and Hayes ? This is Captain Maury's opinion : 

 " These tides," says he, " must have been born in that 

 cold sea, having their cradle about the North Pole." 



But if we carefully consider the theory of the tides 

 this opinion seems inadmissible. Every consideration 

 on which that theory is founded is opposed to the 

 assumption that the moon could by any possibility 

 raise tides in an arctic basin of limited extent. It 

 would be out of place to examine at length the prin- 

 ciple on which the formation of tides depends. It will 

 be sufficient for our purposes to remark that it is not 

 to the mere strength of the moon's " pull " upon the 

 waters of any ocean that the tidal wave owes its origin, 

 but to the difference of the forces by which the various 

 parts of that ocean are attracted. The whole of an 

 ocean cannot be raised at once by the moon ; but if 



